• 한국멀티미디어학회논문지
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• 제23권8호
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• pp.1088-1098
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• 2020

This paper proposes an obstacle avoidance method using a depth polar grid. Depth information is a crucial factor for determining the safe path for collision-free navigation of unmanned aerial vehicles (UAVs) as it can perceive the distance to the obstacles effectively. However, the existing depth-camera-based approaches for obstacle avoidance require computational y expensive path planning algorithms. We propose a simple navigation method using the polar-grid of the depth information obtained from the camera with narrow field-of-view(FOV). The effectiveness of the approach was validated by a series of experiments using software-in-the-loop simulation in a realistic outdoor environment. The experimental results show that the proposed approach successfully avoids obstacles using a single depth camera with limited FOV.

• Ocean Systems Engineering
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• 제7권3호
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• pp.195-223
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• 2017

This paper presents 3D numerical simulations of a Free Standing Hybrid Riser under Vortex Induced Vibration, with prescribed motion on the top to replace the motion of the buoyancy can. The model is calculated using a fully implicit discretization scheme. The flow field around the riser is computed by solving the Navier-Stokes equations numerically. The fluid domain is discretized using the overset grid approach. Grid points in near-wall regions of riser are of high resolution, while far field flow is in relatively coarse grid. Fluid-structure interaction is accomplished by communication between fluid solver and riser motion solver. Simulation is based on previous experimental data. Two cases are studied with different current speeds, where the motion of the buoyancy can is approximated to a 'banana' shape. A fully three-dimensional CFD approach for VIV simulation for a top side moving Riser has been presented. This paper also presents a simulation of a riser connected to a platform under harmonic regular waves.

• Journal of Power Electronics
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• 제18권4호
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• pp.1165-1177
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• 2018

This paper investigates the active damping of grid-connected LCL filter resonance using high-pass filter (HPF) of the grid current. An expression for such HPF is derived in terms of the filter components. This expression facilitates a general study of the actively damped filter behavior in the discrete time domain. Limits for the HPF parameters are derived to avoid the excitation of unstable open loop poles since such excitation can reduce both the damping performance and the system robustness. Based on this study, straightforward co-design steps for the active damping loop along with the fundamental current regulator are proposed. A numerical example along with simulation and experimental results are presented to verify the theoretical analyses.

• Journal of Communications and Networks
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• 제14권6호
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• pp.672-681
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• 2012

A potential breakthrough of the electrification of the vehicle fleet will incur a steep rise in the load on the electrical power grid. To avoid huge grid investments, coordinated charging of those vehicles is a must. In this paper, we assess algorithms to schedule charging of plug-in (hybrid) electric vehicles as to minimize the additional peak load they might cause. We first introduce two approaches, one based on a classical optimization approach using quadratic programming, and a second one, market based coordination, which is a multi-agent system that uses bidding on a virtual market to reach an equilibrium price that matches demand and supply. We benchmark these two methods against each other, as well as to a baseline scenario of uncontrolled charging. Our simulation results covering a residential area with 63 households show that controlled charging reduces peak load, load variability, and deviations from the nominal grid voltage.

• Journal of Electrical Engineering and Technology
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• 제11권6호
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• pp.1527-1534
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• 2016

Online voltage stability monitoring using real-time measurements is one of the most important tasks in a smart grid system to maintain the grid stability. Loading margin is a good indicator for assessing the voltage stability level. This paper presents an Extreme Learning Machine (ELM) approach for estimation of voltage stability level under credible contingencies using real-time measurements from Phasor Measurement Units (PMUs). PMUs enable a much higher data sampling rate and provide synchronized measurements of real-time phasors of voltages and currents. Depth First (DF) algorithm is used for optimally placing the PMUs. To make the ELM approach applicable for a large scale power system problem, Mutual information (MI)-based feature selection is proposed to achieve the dimensionality reduction. MI-based feature selection reduces the number of network input features which reduces the network training time and improves the generalization capability. Voltage magnitudes and phase angles received from PMUs are fed as inputs to the ELM model. IEEE 30-bus test system is considered for demonstrating the effectiveness of the proposed methodology for estimating the voltage stability level under various loading conditions considering single line contingencies. Simulation results validate the suitability of the technique for fast and accurate online voltage stability assessment using PMU data.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 추계 학술대회논문집
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• pp.42-47
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• 1998

The pressure-based methods are very popular in CFD because it requires less computer core memory compared to other coupled or density-based solvers. Currently structured-mesh methodology based on pressure-based algorithm is quite mature to apply to the practical problems. The unstructured mesh method needs much more computer memory than the structured-mesh method. However the pressure-based method utilizing the sequential approach does not require very large memory used for unstructured-mesh density-based solvers. The present study has developed the unstructured grid pressure-based method. Cell-centered finite volume method was selected due to robustness for imposing various boundary conditions and easy implementation of higher-order upwind scheme. The predictive capability of present method has validated against several benchmark problems.

• Asia Pacific Journal of Business Review
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• 제2권1호
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• pp.21-52
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• 2017

Nowadays every technology is becoming smarter. Consequently, intensive use of ICT in the whole industries and cities enables a sustainable approach to meet enormous productivity, efficiency, transparency and conservation of natural recourses. Likewise, the role of ICT in terms of controlling, monitoring in the energy industry allows integrating potential renewables, bulk energy conservation and reliable optimized operation in the entire system. In this paper outlines challenging issues in renewable energy integration in Mongolia and proposes potential recommendations and conclusions. The author investigated the main technologies used in energy industry mainly smart grid, challenges and policy aspect in Mongolian energy sector by using the primary and secondary approach with case studies and literature based methodologies. Based on the policy aspect and current implementation of smart grid, the paper tries to address the readiness for the main application and future potential ICT driven applications. Furthermore, it concluded that ICT convergence is demanded to overcome the current vulnerabilities and significant momentum to leave behind by using its potential energy recourses and favorable geographical state. Policymakers may find this study useful, as it answers the question of whether ICT investment can ultimately reduce energy consumption and may aid in future planning. Even tough, in order to develop a smart grid and integrating renewables firstly set an appropriate market structure, ICT will key enabler to make energy system more profitable and sustainable. Regarding the result of this study, ICT deployment contribution is a huge demand for future opportunities energy in Mongolia.

• 대한임베디드공학회논문지
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• 제9권2호
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• pp.101-107
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• 2014

Mobile robots use an environment map of its workspace to complete the surveillance task. However grid-based maps that are commonly used map format for mobile robot navigation use a large size of memory for accurate representation of environment. In this reason, grid-based maps are not suitable for path planning of mobile robots using embedded board. In this paper, we present the path planning algorithm that produce a secure path rapidly. The proposed approach utilizes a hybrid map that uses less memory than grid map and has same efficiency of a topological map. Experimental results show that the fast path planning uses only 1.5% of the time that a grid map based path planning requires. And the results show a secure path for mobile robot.

• Journal of Communications and Networks
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• 제18권3호
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• pp.484-492
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• 2016

Smart grid (SG) technology is now elevating the conventional power grid system to one that functions more cooperatively, responsively, and economically. When applied in an SG the demand side management (DSM) technique can improve its reliability by dynamically changing electricity consumption or rescheduling it. In this paper, we propose a new SG scheduling scheme that uses the DSM technique. To achieve effective SG management, we adopt a mixed pricing strategy based on the Rubinstein-Stahl bargaining game and a repeated game model. The proposed game-based pricing strategy provides energy routing for effective energy sharing and allows consumers to make informed decisions regarding their power consumption. Our approach can encourage consumers to schedule their power consumption profiles independently while minimizing their payment and the peak-to-average ratio (PAR). Through a simulation study, it is demonstrated that the proposed scheme can obtain a better performance than other existing schemes in terms of power consumption, price, average payment, etc.

• Journal of Computing Science and Engineering
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• 제7권1호
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• pp.44-52
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• 2013

This paper addresses the problem of resource scheduling in a grid computing environment. One of the main goals of grid computing is to share system resources among geographically dispersed users, and schedule resource requests in an efficient manner. Grid computing resources are distributed, heterogeneous, dynamic, and autonomous, which makes resource scheduling a complex problem. This paper proposes a new approach to resource scheduling in grid computing environments, the hierarchical stochastic Petri net (HSPN). The HSPN optimizes grid resource sharing, by categorizing resource requests in three layers, where each layer has special functions for receiving subtasks from, and delivering data to, the layer above or below. We compare the HSPN performance with the Min-min and Max-min resource scheduling algorithms. Our results show that the HSPN performs better than Max-min, but slightly underperforms Min-min.